1. Field of the Invention
The present invention relates to a stroke control apparatus of a reciprocating compressor and a method thereof, and in particular to a stroke control apparatus of a reciprocating compressor and a method thereof which are capable of improving an operational efficiency of a reciprocating compressor by detecting a phase difference between a stroke and a current and varying an operational frequency so as to make an operation distance of a stroke place near TDC (top dead center)=0 in every load variation.
2. Description of the Prior Art
A general reciprocating compressor generates a torque according to rotation of a motor by intermitting power applied to a coil wound around a polyphase stator of the motor by using a switching device and generates a torque according to rotation according to a magnetic sucking force by varying an excitation state between a rotor and a stator gradually.
FIG. 1 is a block diagram illustrating a construction of the conventional stroke control apparatus of a reciprocating compressor.
As depicted in FIG. 1, the conventional stroke control apparatus of the reciprocating compressor includes a reciprocating compressor 10 adjusting a cooling capacity by moving a piston up and down and varying a stroke, a current detecting unit 20 detecting a current generated in the reciprocating compressor 10, a stroke detecting unit 30 detecting a stroke of the piston according to a voltage applied to the reciprocating compressor 10, a phase difference detecting unit 40 detecting a difference value of each phase of the current and the stroke detected in the current detecting unit 20 and the stroke detecting unit 30, a stroke vibration detecting unit 50 detecting stroke vibration by using a variation quantity of the detected phase difference, a stroke control unit 60 detecting the stroke vibration, calculating a stroke occurred in the operation of the reciprocating compressor 10 according to an expected cooling capacity set by a user, comparing the calculated stroke with a reference stroke value inputted by the user in an early operation of the reciprocating compressor 10 and outputting a switching control signal for stroke control, and an inverter 70 receiving a switching control signal for the stroke control and operating the reciprocating compressor 10.
Hereinafter, the operation of the conventional stroke control apparatus of the reciprocating compressor will be described.
First, the piston of the reciprocating compressor 10 performs a linear reciprocation motion by a stroke input voltage according to an initial reference stroke value set by the user, a stroke as an operation distance of the piston is determined by the linear reciprocation motion of the piston, accordingly a cooling capacity is controlled by varying the stroke. Herein, the current detecting unit 20 and the stroke detecting unit 30 detect a current and a stroke of the reciprocating compressor 10.
After that, the phase difference detecting unit 40 detects a phase by using the detected current and stroke, calculates a difference value according to it and judges a stroke vibration by using a variation quantity of the phase difference.
In the early operation of the reciprocating compressor 10, the stroke control unit 60 controls the operation of the reciprocating compressor 10 according to the initial reference stroke value, when a stroke vibration detecting signal is inputted from the stroke vibration detecting unit 50 in the operation of the reciprocating compressor 10, the stroke control unit 60 inputs an inverting signal to the inverter 70.
As described above, an operation control for operating the reciprocating compressor 10 at a maximum efficiency point is performed.
However, since the reciprocating compressor control apparatus according to the prior art has a severe non-linearity in its mechanical motion functions, the operation of the reciprocating compressor can not be performed precisely and accurately by a linear control method without considering the non-linearity. An operational efficiency may be improved by detecting an inflection point of a phase difference between a current and a stroke of the reciprocating compressor and performing an operation control according to it, but when the reciprocating compressor is operated continually, an operational efficiency may be lowered due to a load variation according to changes in surrounding circumstances.